La. Shipley et De. Spalinger, INFLUENCE OF SIZE AND DENSITY OF BROWSE PATCHES ON INTAKE RATES AND FORAGING DECISIONS OF YOUNG MOOSE AND WHITE-TAILED DEER, Oecologia, 104(1), 1995, pp. 112-121
We examined the functional response and foraging behavior of young moo
se (Alces alces) and white-tailed deer (Odocoileus virginianus) relati
ve to animal size and the size and distribution of browse patches. The
animals were offered one, three, or nine stems of dormant red maple (
Acer rubrum) in hand-assembled patches spaced 2.33, 7, 14, or 21 m apa
rt along a runway. Moose took larger twig diameters and bites and had
greater dry matter and digestible energy intake rates than did deer, b
ut had lower cropping rates. Moose and deer travelled at similar veloc
ities between patches and took similar numbers of bites per stem. We f
ound that a model of intake rate, based on the mechanics of cropping,
chewing, and encountering bites, effectively described the intake rate
of moose and deer feeding in heterogeneous distributions of browses.
As patch size and density declined, the animals walked faster between
patches, cropped larger bites, and cropped more bites per stem, and he
nce, dry matter intake rates remained relatively constant. As is chara
cteristic of many hardwood browse stems, however, potential digestible
energy concentration of the red maple stems declined as the size and
number of bites removed (i.e., stem diameter at point of clipping) by
the animals increased. Therefore, the digestible energy content of the
diet declined with decreasing patch size and density. Time spent fora
ging within a patch increased as patch size increased and as distance
between patches increased, which qualitatively supported the marginal-
value theorem. However, actual patch residence times for deer and moos
e exceeded those predicted by the marginal-value theorem (MVT) by appr
oximately 250%. The difference between actual and predicted residence
time may have been a result of(I) an unknown or complex gain function,
(2) the artificial conditions of the experiments, or (3) assumptions
of MVT that do not apply to herbivores.